Tenor mouthpiece and the blank from which it was made.  You can see the difference in the thickness of the rails and the smoothness of the table (and maybe in the evenness of the baffle), but you can’t see the more important difference in the facing curve.

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The most common problems that keep a mouthpiece from performing up to its potential:

• Table isn’t flat
• Facing curve is sub-optimal
• Rails are uneven
• Tip is uneven, or doesn’t match reed